refactor: simplify creating RTCDevice

We were always constructing RTCDevice using a set of metrics that were
defined in the RTC module itself. Don't leak the metrics to other
modules. Instead, create a new() function that always constructs it the
correct way.

Signed-off-by: Babis Chalios <bchalios@amazon.es>

Author: bchalios

src/vmm/src/builder.rs

@@ -13,8 +13,6 @@ use event_manager::{MutEventSubscriber, SubscriberOps};
 use linux_loader::cmdline::Cmdline as LoaderKernelCmdline;
 use userfaultfd::Uffd;
 use utils::time::TimestampUs;
-#[cfg(target_arch = "aarch64")]
-use vm_superio::Rtc;
 
 use crate::arch::{ConfigurationError, configure_system_for_boot, load_kernel};
 #[cfg(target_arch = "aarch64")]
@@ -568,9 +566,7 @@ fn attach_legacy_devices_aarch64(
             .map_err(VmmError::RegisterMMIODevice)?;
     }
 
-    let rtc = RTCDevice(Rtc::with_events(
-        &crate::devices::legacy::rtc_pl031::METRICS,
-    ));
+    let rtc = RTCDevice::new();
     vmm.mmio_device_manager
         .register_mmio_rtc(&mut vmm.resource_allocator, rtc, None)
         .map_err(VmmError::RegisterMMIODevice)

src/vmm/src/device_manager/persist.rs

@@ -449,9 +449,7 @@ impl<'a> Persist<'a> for MMIODeviceManager {
                     )?;
                 }
                 if state.type_ == DeviceType::Rtc {
-                    let rtc = RTCDevice(vm_superio::Rtc::with_events(
-                        &crate::devices::legacy::rtc_pl031::METRICS,
-                    ));
+                    let rtc = RTCDevice::new();
                     constructor_args
                         .resource_allocator
                         .allocate_mmio_memory(

src/vmm/src/devices/legacy/rtc_pl031.rs

@@ -4,6 +4,7 @@
 use std::convert::TryInto;
 
 use serde::Serialize;
+use vm_superio::Rtc;
 use vm_superio::rtc_pl031::RtcEvents;
 
 use crate::logger::{IncMetric, SharedIncMetric, warn};
@@ -59,7 +60,19 @@ pub static METRICS: RTCDeviceMetrics = RTCDeviceMetrics::new();
 
 /// Wrapper over vm_superio's RTC implementation.
 #[derive(Debug)]
-pub struct RTCDevice(pub vm_superio::Rtc<&'static RTCDeviceMetrics>);
+pub struct RTCDevice(vm_superio::Rtc<&'static RTCDeviceMetrics>);
+
+impl Default for RTCDevice {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+impl RTCDevice {
+    pub fn new() -> RTCDevice {
+        RTCDevice(Rtc::with_events(&METRICS))
+    }
+}
 
 impl std::ops::Deref for RTCDevice {
     type Target = vm_superio::Rtc<&'static RTCDeviceMetrics>;